Avian influenza, newcastle disease and infectious bronchitis viruses are pathogens with economical
importance in poultry industry. To determine the role of three mentioned viruses in respiratory diseases
outbreak in Iranian broiler farms, 160 serum samples from 8 broiler flocks with respiratory disease symptoms
were examined by Hemagglutination Inhibition (HI) and ELISA tests. None of these flocks received any of
influenza A, newcastle disease and infectious bronchitis viruses vaccines. The overall antibody titres and
seroprevalence of AIV H9 subtype, newcastle disease and infectious bronchitis viruses in this study were 7.6,
5.34 log2, 1123.12 log10 and 31.2, 18.47, 82.43%, respectively. The results revealed the important role of
infectious bronchitis virus in respiratory disease outbreak in commercial broiler farms of Iran. Therefore, for
preventing the IBV infection in the broiler farms, serotype of the new IBV isolates must regularly be
determined.